Should I put the papers that I contributed only a little to on my CV

Your list of publications has to be complete. You should not omit any papers for which you are an author.

If you are uncomfortable with some items on your list, you may add a note on why you happen to be a co-author, but dropping some work is not a good practice.

In your case, I'd say that there is nothing wrong with these publications: The other authors agreed that your contribution was worth co-authorship and that's usually ok (assuming that the other authors know their field and acted appropriately). If somebody asks about that paper, you can frankly say that you did the calculations but that you can not answer questions about background/other parts or such.

As long as you can describe what your role in the paper was, you are fine. If you didn't play any scientifically relevant role, you shouldn't have been on the paper. Helping with calculations may count as scientific contribution, designing a website not (except for very special cases, e.g. where the website was used to analyse data).

It is not uncommon to have early papers that do not fit with one's later work, and where one doesn't know much about, since one's role was very minor.

I would definitely put them on your CV. The admissions committee for a graduate school would be well aware that the author list order is significant. If they ask you about the paper just guide your answer towards what you contributed. The admission committee probably doesn't really want to know about the paper but rather more about your contributions anyways.